Scanning storage devices include one or more heads, each including a tip that moves relative to a thin film storage medium. The heads and recording medium are located on wafers that are separated by a gap. Regardless of storage mechanism, the head or heads should be mechanically robust, compatible with the storage medium and provide intimate proximity to the storage medium.
One of the challenges in the probe storage area is maintaining accurate spacing between the head and storage medium wafers. In one example, the head-media wafer spacing is 15 μm with head and storage medium wafers that are 13×13 mm2. Variations in this spacing could modify the contact force, angle, and position of the probe head against the storage medium wafer, thus potentially introducing noise during read and write operations, and compromising the reliability of the head and the storage medium mechanical interfacing. In addition, sensors can be embedded in the storage medium and head substrate to sense relative position of the head wafer with respect to the storage medium. Variation in the spacing between the substrates would induce noise in the sensing of the in-plane relative head-media position.
In probe storage devices that do not use micro-electromechanical system (MEMS) actuators and architecture, manufacturing tolerances are expected to result in static variations in head and storage medium spacing from device to device. The stack-up tolerances may include head and storage medium wafer thickness variation, adhesive thickness variation, and manufacturing precision of the actuator and package. These tolerances could be as large as 10 or more microns.
Vibration and shock are expected to result in dynamic changes in the head and storage medium spacing for a given device. In one example, the translation stage to which the storage medium (or the head substrate) is attached is suspended by flexible springs, which allow large linear translation motions. These springs may also allow vertical motions and tilting motions in the presence of external disturbances. Depending on the stiffness of the support springs and the direction of the external forces, the probe heads may bend or lose contact with the storage medium.
To date solutions for non-MEMS probe storage devices have focused on using high-aspect-ratio springs (e.g., having a width-to-thickness>10) to passively maintain head-to-storage medium spacing or actuators to actively control the storage medium wafer. The high-aspect-ratio springs are difficult to manufacture using conventional technology and could not easily provide the required vertical stiffness and horizontal flexibility simultaneously. Increasing out-of-plane stiffness of the support springs therefore would result in increased actuator force requirement and increased actuator power consumption. Active control of vertical translation and two axes of tilt requires additional mechanics and electronics for the actuators and control circuitry, which are prohibitive given the tight space and power budget.
There is a need for a storage apparatus that can maintain the required spacing between the head and storage medium wafers.